I am using DreamPi v1.7 DLE running on a DreamPi from PCWzrd13 (a Raspberry Pi 3 model, I believe) with Wi-Fi. I use the phone number 555-5555 to dial-up. I can successfully play 4x4 Evolution, ChuChu Rocket!, Internet Game Pack, The Next Tetris: On-line Edition, and PSOv2 using the dial-up modem via the DreamPi as well as browse the Web, join IRC, read and send e-mail, etc.
But Alien Front Online gives me problems. (It is a good, official copy that I bought from the GOAT Store. All of the modes run just fine, and yes, I am running it directly from a real GD-ROM.) I can connect to the lobby. I can create a room or select auto-join. The game can download the high scores (jako, dcdingo, etc.). But at the tank selection screen, I get a "connection problems, will retry" kind of a message. After ~20 seconds, I am automatically disconnected. This happens every time. I can get past the tank selection screen by quickly picking a tank and allowing the match to start, but the same situation happens during game-play with the error message and the ~20 second disconnect.
My Pi is normally running at 192.168.1.145. This fully works for all of the other games but only gets me this far with AFO. I have port forwarding enabled (including AFO's port 7980 which I have tried both via UDP-only or UDP with TCP) for all Dreamcast games except for the recently-revived Gundam (see the screenshot for my router's configuration). I have also tried using DMZ instead of port-forwarding. After changing any settings for my DreamPi or router, I have tried leaving them as-is and I have also tried rebooting both of them: all to no avail.
When I set my DreamPi to run at 192.168.1.98 instead of nnn.nnn.n.145 and change the matching settings for ports or DMZ, the problem is even worse whether I am using port forwarding or DMZ. In this case, after dialing-up and verifying my username and password with the DreamPi, I get a "trying to establish a connection to the server" type of a message. It just sits there with that message until the connection attempt times out. I can't connect to the lobby, nor create a room, nor select auto-join, nor download the high scores. I
read from this article a mention of using port 8080 but obviously that port would have been covered when DMZ was enabled for the DreamPi, and it looks like the communication is established with an initial outgoing connection so that shouldn't be affected by port forwarding nor DMZ anyway.
What black magic must I perform to get this game to work online? Please feel free to get technical with your responses. Thank you.